<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        html,body {
            width: 100%;
            height: 100%;
        }

        .main {
            width: 100%;
            height: 100%;
            overflow: hidden;
        }

        .left {
            width: 250px;
            background: #f40;
            float: left;
            position: relative;
        } 

        .right-container {
            float: left;
            width: 100%;
            margin-left: -250px;
            background: #096;
        }

        .right {
            margin-left: 250px;
            background: #369;
        }
    </style>
</head>
<body>
    <div class="main">
        <div class="left">
            left
        </div>
        <div class="right-container">
            <div class="right">
                right
            </div>
        </div>
    </div>
</body>
</html>